As compared with an Out-Cell capacitive touch screen structure, a touch substrate may be omitted from a capacitive touch screen by using the In-Cell touch technology, such that the whole display module may be manufactured in a thinner way. A structural diagram of a liquid crystal display screen using the In-Cell touch technology is shown as FIG. 1 in which touch driving electrodes (Tx) and touch sensing electrodes (Rx) are manufactured on a glass substrate on an array substrate side of the liquid crystal display panel. The Tx lines share same lines with common electrodes (Vcom) lines. Various parasitic capacitances and coupling capacitances may occur in the liquid crystal display screen (i.e. the capacitive touch screen) using the In-Cell touch technology between the Tx and Rx and the Thin Film Transistor (TFT) display devices. In the figure, each of Gate1, Gate2, . . . , Gate n denotes a gate scan line for each line of pixels, respectively; each of Data1, Data2, . . . , Data n denotes a data scan line for each line of pixels, respectively; CLC denotes a capacitance between the liquid crystal display panels; and Cs denotes a storage capacitance.
FIG. 2(a) shows an example of timings for display scanning and touch scanning of an Out-Cell capacitive touch screen, in which a1-a60 denote periods for display scanning and t1-t60 denote periods for touch scanning. As shown in FIG. 2(a), for an Out-Cell capacitive touch screen, the touch scanning is performed in synchronization with the picture refresh since the Out-Cell capacitive touch screen is not affected by TFT driving signals. In other words, the display scanning and touch scanning for a capacitive touch screen are performed in synchronization and they are not affected by each other. As shown, the scanning frequency for the display scanning is 60 Hz, and the scanning frequency for the touch scanning is 100 Hz. FIG. 2(b) shows an example of timings for display scanning and touch scanning of a capacitive touch screen using the In-Cell touch technology, in which a1-a60 denote periods for display scanning and t1-t60 denote periods for touch scanning. As shown in FIG. 2(b), the In-Cell touch technology utilizes a scanning mode in which the scanning is performed in a blank interval between two frames of pictures. In other words, the display scanning and touch scanning for the liquid crystal display screen shall be performed in a time-sharing manner. As shown, the scanning frequency for the display scanning is 40 Hz, and the scanning frequency for the touch scanning is 40 Hz.
A system block diagram of a liquid crystal display screen using the In-Cell touch technology is shown as FIG. 3. Touch scanning time, t, assigned to each frame is limited due to the limitation of data transmission rates of the timing controller and driver and charging time of sub-pixels. When t is small, scannings of Tx and Rx cannot be finished, and therefore t is to be increased appropriately. Currently, the direct way to increase t is to increase the scanning time of a frame, and the assigned touch scanning time is increased accordingly. However, this will lead to a lower frame rate, and the quality of the picture will be deteriorated. Flickering, smearing, or the like will occur.
In summary, since a liquid crystal display screen using the In-Cell touch technology utilizes a time-sharing driving method, the liquid crystal display screen cannot operate at a higher display refresh rate when there is no touch.